MX2007001666A

MX2007001666A - Method for treating extremely small particles of polyethylene terephthalate.

Info

Publication number: MX2007001666A
Application number: MX2007001666A
Authority: MX
Inventors: Donald W Hayward; Daniel L Witham
Original assignee: Phoenix Technologies Int
Priority date: 2004-08-11
Filing date: 2005-08-09
Publication date: 2007-04-10
Also published as: EP1776392A4; AU2005272930B2; EP1776392A2; WO2006020603A3; AU2005272930A1; CA2576336A1; US7579431B2; WO2006020603A2; BRPI0514224A; US20080021194A1

Abstract

A method for treating extremely small particles of recycled polyethylene terephthalate comprises providing a quantity of RPET particles having an average mean particle size ranging from about 0.0005 inch to about 0.05 inch in diameter, heating the RPET particles to a temperature sufficient to cause at least a portion of the RPET particles to adhere to one another, and forming the adhered RPET particles into pellets, said pellets having substantially the same average surface-to-volume ratio as the bulk, un-adhered RPET particles.

Description

METHOD FOR TREATING EXTREMELY SMALL PARTICLES OF POLYETHYLENE TEREFTALATE CROSS REFERENCE TO RELATED REQUESTS This application claims the benefit of the U.S. Provisional Patent Application. Serial Number 60 / 600,585, filed August 11, 2004. FIELD OF THE INVENTION The present invention relates generally to a method for treating extremely small particles of polyethylene terephthalate (PET). More particularly, the invention is directed towards a process for treating recycled polyethylene terephthalate (RPET = Recycled Polyethylene Terephthalate) particles, to prepare stock material that is easier to handle than fine powder, which substantially retains the operability of the process and the utility exhibited by extremely small RPET particles. BACKGROUND OF THE INVENTION It has recently been discovered that extremely small RPET particles inexplicably exhibit superior processing properties for the production of new plastic articles. The US Patents Numbers 5,734,234 and 5,899,399, for example, disclose that extremely small RPET particles produced by the fragmentation of RPET granules can be easily decontaminated and recycled to produce plastic containers. However, extremely small RPET particles are difficult to transport and otherwise handle. Generally, the handling of fine powders requires specialized equipment such as custom vacuum transport systems, dense phase conveyors, crystallizers, dryers, containers, tanks, and blastholes. Such transport equipment is very expensive, and expensive to operate and maintain. For these reasons, manufacturers prefer to use RPET in flakes or larger pellets or pellets and conventional handling equipment in the manufacture of plastic articles, but in this way they lose the benefits that could otherwise be realized by the manufacturer. use of extremely small RPET particles. It would be desirable to treat extremely small RPET particles to prepare storage material that is easy to handle in conventional process equipment, which substantially retains the advantages of the process, operability, and utility exhibited by extremely small RPET particles. SUMMARY OF THE INVENTION In accordance with the present invention, SE has discovered a process for treating extremely small RPET particles to surprisingly improve handleability. The process comprises the steps of providing a quantity of RPET particles having an average particle size in the range from about 0.0127 mm (0.0005 inch) to about 1.27 mm (0.05 inch) in diameter, heating the RPET particles at a temperature sufficient to cause a portion of the RPET particles to adhere to one another, and to form the RPET particles in granules, said granules having substantially the same average surface-to-volume ratio as compared to virgin resin granules or recycled in bulk. The process of the invention is particularly useful for preparing RPET granules whose process advantages, operability, and utility are essentially identical to extremely small RPET particles in bulk, for the final production of plastic articles such as containers. BRIEF DESCRIPTION OF THE DRAWINGS The novel features that are considered characteristic of the invention are presented with particularity in the appended claims. The invention by itself, however, will be better understood with the descriptions accompanying the specific embodiments when read in conjunction with the drawings that serve, wherein: Fig. 1 is a fragmentary elevation view, partially sectioned, of an apparatus for treating extremely small RPET particles, including a device for heating the RPET particles, extruding the heated and adhered RPET particles, and cutting the extrusions to form granules; Fig. 2 is a fragmentary sectional view along line 2-2 of Fig. 1; and Fig. 3 is an enlarged fragmentary view of the heated die forming passages illustrated in Fig. 1. DETAILED DESCRIPTION OF THE PREFERRED MODE An amount of RPET particles having an average particle size in the range from about of .0127 mm (0.0005 inch) to about 1.27 mm (0.05 inch) in diameter, according to the present invention. These extremely small RPET particles can be formed by grinding or otherwise fragmenting readily available RPET flakes or flakes, using conventional equipment such as mills, ball mills, impact mills, cryogenic mills, pulverizers, grinding or grinding mills, and similar. A preferred particle size for the RPET particles is about .254 mm (0.01 inch) in diameter (approximately 300 microns). These dust-like RPET particles are very difficult to transport otherwise handled. The RPET particles are heated to a temperature sufficient to cause at least a portion of the RPET particles to adhere to one another. Referring now to the drawings, and particularly Figs. 1 and 3, there is shown the apparatus 10 for forming the RPET particles, according to the present invention. It comprises a bushing having a plurality of die passages 14 through which the RPET particles move to form rod-shaped extrusions 16. Although, die passages in circular sectional cut 14 are illustrated in the drawings, the grains The resulting diameters represented by the arrows 30 in FIG. 3, will be readily apparent to those with ordinary skill in the art that other sectional cut configurations (not shown) can be used. The RPET particles are heated to or slightly above the glass transition temperature (TG) of the RPET from which the particles were derived. Generally, the glass transition temperature for RPET particles is greater than about 70 degrees Celsius. The particles are heated by frictional coupling until at least a portion of them adhere to each other by contact point between them. Therefore, the particles essentially retain their general forms, and the interstitial spaces between the particles are likewise retained in the adhered mass. RPET particles are formed in granules , said granules 20 have substantially the same average surface-to-volume ratio as the granules of RPET particles, non-adhered, in bulk 18. Although cylindrical granules 20 are illustrated in the figures, the term "granule" is contemplated for including all forms of sintered RPET particles 18 including, for example, flakes or flakes, spheres, cubes, shapeless pieces, and the like (not shown). As it will be readily apparent to someone with ordinary skill in the art, the configuration of the "granules" will be determined by the process and equipment used to heat and form them. Figs. 1, 2, and 3 illustrate that the die passages 14 are provided with an initial funnel-shaped inlet 22, to assist in the formation of the extrusions 16. Alternatively, the initial portions of the die passages 14 may be provided with entries in different ways, or without any (not shown). The adhered RPET particles are driven by suitable and conventional means, (such as pistons, rollers, forced gas, gravity, and the like) through the passages of the die 14 in the direction of the arrow 24 shown in Fig. 3 for producing the extrusions 15 of the adhered RPET particles. The frictional engagement between the individual particles and the walls 22 creates sufficient thermal energy so that the adjoining surfaces of the particles in contact with the walls 22 reach the glass transition temperature and tend to adhere to each other. This adhesion causes at least that the outer layers of the particles form a granular shell around the central mass of the non-adhering particles forming the extrusions 18. The extrusions 16 comprise at least partially sintered RPET particles are caused to advance to an adjacent section of the instrument 10 referred to as the relief section 26, where the walls of the die passage 14 tend to diverge in the elongated cones configurations inverted as they extend toward the exits of the passages of the die 14. The extrusions 16 from there they are caused to exit the passages of the die 14. A cutting knife 28 is caused to travel the exit area of the passages of the die 14, to cut the extrusions 16, hence forming the granules 20 of the RPET particles Sintered The length of the. granules 20 is determined by the synchronization of the cutting knife 28 transverse with the speed of movement of the extrusions 16. The granules 20 fall by gravity onto a collecting surface which may comprise, for example, a movable conveyor,. a collection container, a conduit that leads, to another equipment, or something similar. Conveniently, the sintered granules can then be transported by conventional non-specialized equipment. This form of RPET retains the advantages of the process, operability, and utility of extremely small RPET particles, but eliminates the difficulties and costs associated with transportation and handling of powder-like materials. The granules reflect the characteristics of the RPET particles; in which the granules exhibit a very fast drying time, accelerated diffusion for the removal of contaminants or the infusion of adjuvants, faster growth rates by intrinsic viscosity during the subsequent processes of solid-state, etc. The bushing 10 can be heated by conventional means such as, for example, electrical resistance heating, flame heating, infrared radiant heating, hot gas heating, and the like. The bushing 12 is heated in such a manner that the bulk RPET particles 18 contained within bushing 12 acquire, by friction between the particles or by conduction and / or convection of the thermal energy of the bushing 12, a temperature sufficient to cause at least that a portion of the RPET 18 particles adhere to each other. The invention will be more readily understood by reference to specific embodiments described above, which are representative of the invention. It should be understood, however, that the specific modalities are provided only for the purpose of illustration, and that the invention can be practiced other than that which is specifically illustrated without departing from its spirit and scope.

Claims

CLAIMS 1. A process for the treatment of extremely small RPET particles, comprises providing a quantity of RPET particles having an average particle size in the range from about 0.0127 mm (0.0005 inch) to about 1.27 mm (0.05). inch) in diameter; heating the RPET particles to a temperature sufficient to cause at least a portion of the RPET particles to adhere to each other; and forming the RPET particles adhered to granules, said granules have substantially the same • ratio of surface area to average volume as non-adhered RPET particles, in bulk.
2. The process according to claim 1, characterized in that the average particle size of the RPET particles is about .254 mm (0.01 inch) in diameter.
3. The process according to claim 1, characterized in that the heating is carried out by heating by electrical resistance, heating by flame, infrared radiant heating, or heating with hot gas.
4. The process according to claim 1, characterized in that the heating is carried out by frictional coupling between the particles.
5. The process according to claim 1, characterized in that at least some of the RPET particles are heated to a temperature greater than or equal to the glass transition temperature.
6. The process according to claim 1, characterized in that the RPET particles are heated to a temperature higher than about 70 degrees Celsius.
The process according to claim 1, characterized in that the granules are formed into cylinders, flakes, spheres, cubes, or pieces without form.
8. The process according to claim 1, characterized in that the granules are formed by passing heated RPET particles through passages of a die.
9. A process for treating extremely small RPET particles, characterized in that it comprises: providing a quantity of RPET particles having an average particle size of about .254 mm (0.01 inch) in diameter; heating the RPET particles, by frictional coupling, electric resistance heating, flame heating, infrared radiant heating, or heating with hot gas, at a temperature greater than or equal to the glass transition temperature, to cause at least a portion of the RPET particles adhere to each other; and forming the RPET particles adhered to granules in the form of cylinders, flakes, spheres, cubes, or shapeless chunks, by passing the heated RPET particles through die passages, said granules having substantially the same proportion of surface at average volume as 0 RPET particles not adhered, in bulk.
10. The process according to claim 9, characterized in that the RPET particles are heated to a temperature greater than about 70 degrees Celsius.
11. A process for treating extremely small RPET particles, comprising: providing a quantity of RPET particles having an average particle size of about .254 mm (0.01 inch) in diameter; heating the RPET particles, by frictional coupling, electric resistance heating, flame heating, infrared radiant heating, or heating with hot gas, at a temperature greater than about 70 degrees Celsius, to cause at least a portion of the RPET particles adhere to each other; and forming the RPET particles into granules in the form of cylinders, flakes, spheres, cubes, or shapeless chunks, by passing the RPET particles through passages of the die, said granules having substantially the same proportion of surface at average volume as RPET particles not adhered, in bulk.